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- 주제어 : atomistic thermodynamics (검색결과 3 건)
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Kwon, K.D.,Newton, A.G. Pergamon Press ; Elsevier Science Ltd 2016 Geochimica et cosmochimica acta Vol.190 No.-
<P>The surfaces of clay minerals, which are abundant in atmospheric mineral dust, serve as an important medium to catalyze ice nucleation. The lateral edge surface of 2:1 clay minerals is postulated to be a potential site for ice nucleation. However, experimental investigations of the edge surface structure itself have been limited compared to the basal planes of clay minerals. Density functional theory (DFT) computational studies have provided insights into the pyrophyllite edge surface. Pyrophyllite is an ideal surrogate mineral for the edge surfaces of 2: 1 clay minerals as it possesses no or little structural charge. Of the two most-common hydrated edge surfaces, the AC edge, (110) surface in the monoclinic polytype notation, is predicted to be more stable than the B edge, (010) surface. These stabilities, however, were determined based on the total energies calculated at 0 K and did not consider environmental effects such as temperature and humidity. In this study, atomistic thermodynamics based on periodic DFT electronic calculations was applied to examine the effects of environmental variables on the structure and thermodynamic stability of the common edge surfaces in equilibrium with bulk pyrophyllite and water vapor. We demonstrate that the temperature-dependent vibrational energy of sorbed water molecules at the edge surface is a significant component of the surface free energy and cannot be neglected when determining the surface stability of pyrophyllite. The surface free energies were calculated as a function of temperature from 240 to 600 K and water chemical potential corresponding to conditions from ultrahigh vacuum to the saturation vapor pressure of water. We show that at lower water chemical potentials (dry conditions), the AC and B edge surfaces possessed similar stabilities; at higher chemical potentials (humid conditions) the AC edge surface was more stable than the B edge surface. At high temperatures, both surfaces showed similar stabilities regardless of the water chemical potential. The equilibrium morphology of pyrophyllite crystals is also expected to be dependent on these two environmental variables. Surface defects may impact the surface reactivity. We discuss the thermodynamic stability of a possible Si cation vacancy defect which provides additional hydroxyl group on the surface. (C) 2016 Elsevier Ltd. All rights reserved.</P>
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이병주 대한금속·재료학회 2018 대한금속·재료학회지 Vol.56 No.4
Computational approaches such as first-principles calculations, atomistic simulations, phase field simulations, computational thermodynamics and finite element method simulations are widely used in the metals and materials community. Even with their successful applications for better understanding of material phenomena, and the design of new materials or processes, a gap remains between the results of computational approaches and experimental data. This gap originates with differences in the computational and experimental conditions, and limits the wider application of computational approaches. In this review article, some successful examples of computational materials and process design are outlined, focusing on ways to utilize the results of computational approaches. It will be emphasized that it is more important to clarify the governing mechanism of materials phenomena from the effects of individual experimental variables on simulation results rather than make an effort to obtain good agreement between simulations and experiments with phenomenological issues. It will be also emphasized that research efforts to extend the applicability of the computational approaches are continuously required.
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